In general, a super conductive wire is composed of a super conductive material such as Ni-Ti, Nb.sub.3 Sn, and the like, and a stabilizing material such as copper, aluminum, and the like, The super conductive wire is wound in the form of a coil to produce a magnetic field and is used as an electromagnet for a nuclear fusion reactor and an accelerator in high physical science. However, it has been well known that the super conductive wire deteriorates in its operational characteristics, as shown in FIG. 1, when it is made into a coil. The cause thereof can be classified into two large groups. The one is a heat evolution due to a disturbance (internal disturbance) raised in the interior of the super conductor and the other is the fact that a heat evolution (external disturbance) due to friction among the super conductive wires in a coil becomes higher than the critical temperature of the super conductor to bring about a transition of from super conductive state to normal conductive state. The former has been solved by making the super conductive material have a small diameter, but the latter has not yet been solved.